This invention relates to a lenticular lens screen constituting a transmission type screen used for a rear projection apparatus.
For the rear projection apparatus, the wide horizontal audience coverage and the even brightness of the image are required. To realize this requirement, it is necessary for the transmission type screen to horizontally and sufficiently diffuse the light projected to the screen.
A lenticular lens screen is used for this purpose as one optical element to diffuse the projected lights. In a prior art, a lenticular lens arrangement is located only on the light incident side of the screen, and the diffusion of the outgoing light has been controlled by the arrangement of the lenticular lens assembly, each unit lens, i.e. lenticle, having a section approximately semicircular or elliptical.
Recently, a screen provided with the lenticular lens arrangement on the light outgoing side has been proposed such as disclosed in the Japanese Patent Laid-open (KOKAI) No. 58-134627, in which the lenticular lens arrangement on the light outgoing side of the screen is located on a light focused surface of the lenticular lens arrangement on the light incident side. The purpose of the lenticular lens arrangement on the light outgoing side is not to diffuse the light but to compensate for an inclination of the light projected obliquely with respect to the optical axis of the lenticular lens by the coma aberration generated by the lenticular lens arrangement on the light incident side of the screen.
As described above, in the conventional technique of the lenticular lens screen, the light diffusion depends only on the lenticular lens arrangement located on the light incident side, and for this reason, in order to increase the degree of the outgoing light diffusion, it is necessary to elongate, in the optical axis direction, the sectional shape of a unit lens (called hereinafter a lenticle) constituting the lenticular lens arrangement on the light incident side.
The elongation of the sectional shape of the lenticule will cause the following significant problems.
(a) It is difficult to produce a mold to be used for manufacturing a screen and the durability of the thus produced mold is not good.
(b) In case the screen is formed by an extrusion molding method with high productivity, the shape of the designed lens is not desirably realized.